Notes on blocking spam by filtering on ASN
So now that I can classify IP (Internet Protocol) addresses by ASN (Autonomous System Number) [1], I thought I might see how it could help with spam email. I'm already using an ansi-spam agent [2] to cut down on spam, so maybe filtering by ASN could cut down even more. The last time I looked into additional means of spam avoidance, the use of SPF (Sender Policy Framework) wasn't worth the effort [3].
And I'm afraid the effort of blocking via ASN won't be worth the effort either. Looking over email attempts over the past month, the top 10 networks who sent email to my server, from 5,181 individual emails:
Table: Top 10 emailers to my server AS (Autnonmous System) Count ------------------------------ IOMART-AS, 375 IDNIC-IDCLOUDHOST-AS-ID 369 PAIR-NETWORKS, 263 MICROSOFT-CORP-MSN-AS-BLOCK, 246 AS-COLOCROSSING, 152 EMERALD-ONION, 124 GOOGLE, 122 SPARKPOST, 120 TZULO, 112 AMAZON-02, 106
Unlike the web (or even Gemini or gopher) there isn't one dominant network here—it's all spread out. I don't think it's really worth the effort to block via ASN for spam. At least for my email server.
[2] https://github.com/spc476/x-grey
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